1. Field of the Invention
The present invention relates to a transfer press in which a workpiece is transferred between successive work stations in a multi-station process performed in the press.
2. Description of the Prior Art
In a conventional transfer press, there is provided a two-dimensional transfer system for driving a pair of feed bars so as to have the feed bars perform an advancing/returning and a clamping/unclamping operation on a workpiece, so that the workpiece is sequentially transferred to a plurality of dies disposed in successive work stations on a bolster. In case of a three-dimensional transfer system for driving the feed bars of the press, in addition to the advancing/returning and the clamping/unclamping operation of the workpiece, the feed bar is further driven vertically to perform a lifting/lowering operation on the workpiece. For facilitating an exchange of the dies in the press, the bolster may be taken out of the press while carrying the dies thereon. The bolster of this type is a so-called "moving bolster".
A three-dimensional transfer system 10 and a so-called moving bolster 3, of the conventional transfer press are shown in construction in FIGS. 7 and 8.
In FIG. 7, the moving bolster 3 is provided with a plurality of work stations denoted by the reference characters: Nos. 1 to 6. The moving bolster 3 may be taken out of the press in directions Y1 and/or Y2, while traveling in these directions by means of tires/rails (not shown). As is clear from FIG. 7, the size of the press in plan view is determined by a space between each pair of columns 1 the number of which is four.
As shown in FIG. 7, a clamping/unclamping unit 30 forming a part of the three-dimensional transfer system 10 moves four cradles 12 (which carry the pair of the feed bars 11 thereon) back and forth in a direction Y to have the feed bars 11 perform the clamping/unclamping operation of the workpiece. On the other hand, a lifting/lowering unit 40 of the transfer system 10 is so formed as to be integral with the clamping/unclamping unit 30, and moves the cradles 12 back and forth in a direction Z (shown in FIG. 8) to have the feed bars 11 perform the lifting/lowering operation of the workpiece. Further, an advancing/returning unit 20 of the transfer system 10 is provided in an area adjacent to end portions of the feed bars 11, and connected with pins lip (shown in a left-hand end area of FIG. 7). The pins 11P ape provided in the above end portions of the feed bars 11, and moves the feed bars 11 back and forth in a direction X to have the feed bars 11 perform the advancing/returning operation on the workpiece.
These operations on the workpiece performed by the feed bars 11 follow a transfer mode shown in FIGS. 6(A) and 6(B). Since the feed bars 11 ape mounted on the cradles 12 so as to be slidably movable in the direction X relative to the cradles 12, it is possible fop the feed bars 11 to perform each of the above operations independently or simultaneously during a part of the mode.
In the above construction of the transfer system 10 comprising the units 20, 30 and 40, the feed bars 11 are provided with fingers, and perform the above operations through suitably selected ones of various drive mechanisms, for example such as a rack/pinion drive mechanism, a crank-arm drive mechanism, a drive-lever mechanism, a planetary-gear drive mechanism and the like by using torque transmitted through cams, levers and rods fixedly mounted on a crank shaft or a slider of the press. Consequently, as shown in FIGS. 7 and 8, each of the units 20, 30 and 40 is fixedly mounted in a space between the columns 1.
Incidentally, in case the transfer system 10 is driven by servo-motors in a conventional manner, the same drive mechanisms as those described above may be used. In FIG. 7, the reference numeral 9 denotes an unloader of outlet conveyer of the workpiece. In FIG. 8, the reference numeral 2 denotes a bed of the press.
In an operation of exchanging the dies on the moving bolster 3 in the conventional press, it is also necessary for the press to simultaneously perform an exchanging of fingers (which are fixedly mounted on the feed bars 11) so as to have the current fingers replaced with fingers corresponding to a new workpiece. Namely, in order to replace the current fingers with the fingers corresponding to the new workpiece, the feed bars 11 are supported by holding members 3P (shown in two-dotted chain lines in FIG. 8) and taken out of the press by the same members 3P. At this time, since opposite ends of each of the feed bars 11 are connected with the transfer system 10 (i.e., with the units 20 and/or 30, 40), it is impossible for the conventional press to take the entire feed bars 11 out of the press together with the bolster 3.
In order to solve the above problem, in another conventional transfer press, there has been proposed a pair of split-type feed bars each of which is divided into three members: a movable feed bar 11 being on the side of the moving bolster 3; and, a pair of stationary feed bars 11R fixedly mounted on the transfer system 10 (i.e., on the units 20, 30 and 40). The movable feed bar 11 is connected with each of the stationary feed bars 11R through a splitting mechanism 11S so as to be integral with the stationary feed bars 11R during the multi-station process performed in the press, and separated from the stationary feed bars 11R when the movable feed bars 11 are taken out of the press together with the moving bolster 3.
The entire length of each of the feed bars (11, 11S, 11R) constructed of the movable ones 11, splitting mechanisms 11S and the stationary feed bars 11R is determined by the number of the work stations of the press and a feed stroke in the advancing/returning operation of the workpiece. Consequently, the entire longitudinal length of the press or a space between the columns 1 in the direction X of the press is determined by the above entire length of the feed bar (11, 11S, 11R).
Therefore, the conventional transfer press provided with the moving bolster 3 and the three-dimensional transfer system 10 comprising the units 20, 30 and 40 suffers from the following problems (1) to (6):
(1) When the number of the work stations and the feed stroke of the workpiece are determined, a space between the columns 1 is automatically determined. Consequently, it is impossible for the conventional transfer press to reduce the thus determined space between the columns 1, which makes it impossible to downsize the transfer press itself. PA1 (2) In case that the feed bars 11 are carried by the holding members 3P on the side of the moving bolster 3 when the feed bars 11 are taken out of the transfer press, there is a possibility that the feed bars 11 may fall down on the side that the fingers are mounted portion due to the weight of the fingers. PA1 (3) Even after the feed bars 11 are taken out of the transfer press together with the moving bolster 3, it is necessary for the operator of the press to manually move the heavy feed bars 11 before both of an exchange of the dies and an exchange of the fingers are conducted. However, such manual work for moving the feed bars 11 is very hard and risky. Particularly, it is difficult to reduce the working time required in the manual work, which makes it impossible to satisfy the current need for further improving the transfer press in efficiency. PA1 (4) Since it is impossible to conduct dynamic adjustments of the feed bars 11 including the finger's alignment operation in a condition in which the moving bolster 3 is taken out of the press, it takes too much time to ensure the press in reproducibility of the process after completion of the die exchange. PA1 (5) The conventional transfer press is poor in versatility since the press is integral with the transfer system 10 comprising the units 20, 30 and 40. PA1 (6) When any one of the constituent elements of the clamping/unclamping unit 30 (for example) of the conventional transfer press fails, it is necessary to stop the whole of the press in operation. PA1 each of the feed bars is constructed of a movable feed bar element and a stationary feed bar element; and PA1 the transfer system comprises: a plurality of second casings the number of which is four, each of the second casings being fixedly mounted on each of four corner portions of the bolster; a plurality of first casing the number of which is four, each of the first casings being mounted on a respective one of the second casings so as to be vertically movable relative thereto; a lifting/lowering unit for each pair of first and second at a respective corner portion of the bolster, each lifting/lowering unit; provided with a first motor and a first threaded shaft operably connected with the first motor for driving of the first casing so as to have the same lifted and lowered relative to each of the second casings, the first motor being fixedly mounted on each of the second casings; a clamping/unclamping unit provided with a second motor and a second threaded shaft operably connected with the second motor for driving the stationary feed bar element so as to perform the same clamping/unclamping operation on the workpiece, the second motor being fixedly mounted on each of the first casings; and, an advancing/returning unit provided with a third motor and a third threaded shaft operably connected with the third motor for driving the movable feed bar element so as to have the same perform the advancing/returning operation of the workpiece, the movable feed bar element being moved relative to the stationary feed bar element in the advancing/returning operation, the third motor being fixedly mounted on each of the first casings which are aligned in a longitudinal direction of the transfer system. PA1 each of the feed bars is not of a split type constructed of a plurality of feed bar elements aligned with each other in series in a longitudinal direction of the transfer system, but of an integrated type in which the movable feed bar element and the stationary feed bar element are arranged in parallel with each other so as to minimize the entire longitudinal length of each of the feed bars.
Incidentally, in order to solve the above falling-down problem, there have been proposed various types of the conventional holding members 3P, for example such as ones provided with: fastening magnets; fastening screws; fastening springs; and like fastening means; in addition to ones using the weight oft the feed bars 11 to have the bars 11 engaged with the holding members 3P under the influence of gravity (hereinafter referred to as the gravity type: see Japanese Utility Model Publication No. Sho 62-457766). However, any one of the conventional holding members 3P suffers from its inherent problem. Namely, in the holding members 3P of the fastening-magnet type, there is a fear that the holding members 3P attract iron objects. In addition, the holding members 3P oft this type has a tendency to deteriorate in their holding power with the lapse of time. On the other hand, in the holding members 3P of the fastening-screw type, this type takes too much time in operation. In addition, it is hard to automatically operate this fastening-screw type of the holding members 3P. In case of the holding members 3P of the gravity type, since the holding power of such members 3P largely depends on the weight of the feed bars 11, it is impossible to downsize the feed bars 11.